Willow cuts methane by 27%, NI study finds

Methane emissions from cattle fell by over a quarter when they grazed a willow plantation on the Gilliland farm near Derry city, a new study has found.

The research trial was conducted on Brook Hall Estate and was led by PhD student Josh Thompson from Queen’s University Belfast.

Speaking at the site on Tuesday, Thompson explained that willow contains natural chemicals called condensed tannins which, when consumed by cattle, suppress methane production in the rumen.

Cattle performance

As part of the trial, the performance of the dairy-cross cattle was compared to that of similar cattle grazing perennial ryegrass on the Foyle Food Group’s farm near Cookstown.

“Crude protein of willow is 17% and it was 18% for the grass. The metabolisable energy was slightly lower for willow at 9.2MJ/kg, whereas grass was about 10.6MJ/kg,” Thompson said.

A portable respiration chamber was used to measure emissions from cattle on both sites and it found methane production was 27% lower when cattle grazed willow.

However, the animals on the willow put on less weight, with their daily liveweight gain averaging 0.7kg, compared to 1.0kg/day on grass.

“The reason for the difference was because we rotationally grazed this willow platform. In the second grazing, there was a significant difference in the willow yield available for cattle,” Thompson said.

Energy crop

The willow was originally planted by farm owner Professor John Gilliland, 28 years ago, and has been harvested as a biomass energy crop nine times since then.

For the cattle grazing study, the plantation was sub-divided with electric fencing, and cattle were given an allocation for five to seven days.

Each strip of willow was left to re-grow for six to seven weeks between two grazings last year. The trial is being repeated this year, with the aim of getting three grazings across the season.

Gilliland remarked that cattle were surprisingly content as they grazed the tall, dense willow plants and his plan is to set up more grazing trials on the farm.

“I want to hybridise it to have grasses, herbs and willow in the same space as nature-based solutions. My vision for Brook Hall is to have a living lab,” he said.

Greenhouse gas emissions from all farms on the ArcZero project fell considerably when the carbon dioxide captured by soils, trees and hedgerows was measured and accounted for.

Across the seven NI farms, the process of carbon sequestration led to a 27% reduction on two dairy farms, with a 31% drop observed on a beef and sheep farm.

Emissions were reduced by 56% on a sheep farm and by 59% on an arable farm when carbon sequestration was accurately measured.

‘Net zero’ reached

It put two farms beyond “net zero” emissions, meaning the farms are already capturing more carbon than they are emitting.

One of these farms has a fifth of the land area planted in trees and the other farm, which is Brook Hall Estate, has half the area planted in willow and another quarter is woodland.

“A target of net zero by 2050 is about the average of the industry, which assumes that some will go beyond net zero and some won’t get there at all,” said Professor John Gilliland.

“Surprisingly, some farms are already there, but that’s never talked about. You won’t know where you are until you go measure, so know your numbers,” he added.

Carbon measuring

Speaking at a farm walk on Tuesday, Gilliland expressed frustration that many carbon footprint calculators for farms do not account for the carbon that is removed from the atmosphere and stored in soil, trees and hedgerows.

Likewise, the national system for counting emissions, known as the Greenhouse Gas Inventory, does not attribute carbon sequestration on farms to the agriculture sector.

Instead, these figures are included in the land use sector.

“If I build soil carbon or plant more hedges, is that accounted for in the inventory? Not at the moment, it’s not. Policymakers have a lot of catching up to do,” Gilliland said.

Soils are responsible for 97% of all the carbon that is stored across the seven ArcZero farms, results from the project indicate.

Each of the farms were soil-sampled, carbon-benchmarked and mapped with LiDAR technology to quantify where carbon was stored.

On Brook Hall Estate, soil samples were taken to an average depth of 0.86m.

Results showed that 42% of total carbon stored below permanent grassland is in the top 15cm; 23% is between 15 and 30cm, and 35% is below 30cm.

Silvopasture

There are five different types of land use on the farm and silvopasture, where animals graze grass between trees, had the highest soil carbon stocks at over 150t/ha.

Silvopasture beat both a 30-year-old woodland and a 250-year-old woodland for soil carbon. The lowest soil carbon stock was seen in grassland, although it still stood at over 120t/ha.

However, grassland outperformed the other four land uses when it came to every measure of biological activity in soils.

Grassland’s average earthworm count was almost eight times higher than silvopasture, and 20 times higher than the willow plantation. There were effectively no earthworms found in woodland.

The soils under grassland also scored highest for measures of soil respiration and decomposition rate.